Re: [PATCH v6 39/44] KVM: VMX: Bug the VM if either MSR auto-load list is full

["Mi, Dapeng" <dapeng1.mi@linux.intel.com>]

On 12/6/2025 8:17 AM, Sean Christopherson wrote:
> WARN and bug the VM if either MSR auto-load list is full when adding an
> MSR to the lists, as the set of MSRs that KVM loads via the lists is
> finite and entirely KVM controlled, i.e. overflowing the lists shouldn't
> be possible in a fully released version of KVM.  Terminate the VM as the
> core KVM infrastructure has no insight as to _why_ an MSR is being added
> to the list, and failure to load an MSR on VM-Enter and/or VM-Exit could
> be fatal to the host.  E.g. running the host with a guest-controlled PEBS
> MSR could generate unexpected writes to the DS buffer and crash the host.
>
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
>  arch/x86/kvm/vmx/vmx.c | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 38491962b2c1..2c50ebf4ff1b 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -1098,6 +1098,7 @@ static void add_atomic_switch_msr(struct vcpu_vmx *vmx, unsigned msr,
>  {
>  	int i, j = 0;
>  	struct msr_autoload *m = &vmx->msr_autoload;
> +	struct kvm *kvm = vmx->vcpu.kvm;
>  
>  	switch (msr) {
>  	case MSR_EFER:
> @@ -1134,12 +1135,10 @@ static void add_atomic_switch_msr(struct vcpu_vmx *vmx, unsigned msr,
>  	i = vmx_find_loadstore_msr_slot(&m->guest, msr);
>  	j = vmx_find_loadstore_msr_slot(&m->host, msr);
>  
> -	if ((i < 0 && m->guest.nr == MAX_NR_LOADSTORE_MSRS) ||
> -	    (j < 0 &&  m->host.nr == MAX_NR_LOADSTORE_MSRS)) {
> -		printk_once(KERN_WARNING "Not enough msr switch entries. "
> -				"Can't add msr %x\n", msr);
> +	if (KVM_BUG_ON(i < 0 && m->guest.nr == MAX_NR_LOADSTORE_MSRS, kvm) ||
> +	    KVM_BUG_ON(j < 0 &&  m->host.nr == MAX_NR_LOADSTORE_MSRS, kvm))
>  		return;
> -	}
> +
>  	if (i < 0) {
>  		i = m->guest.nr++;
>  		vmcs_write32(VM_ENTRY_MSR_LOAD_COUNT, m->guest.nr);

Reviewed-by: Dapeng Mi <dapeng1.mi@linux.intel.com>